1. Field of the Invention
The present invention relates to a computer architecture and method which can conserve power. More particularly, this invention relates to an architecture which allows a computer to suspend operation for a period of time and resume operation later in order to conserve overall power consumption.
2. Background Information
In certain applications like control systems, microprocessors are used for real-time monitoring and control. Information is typically sampled and updated continuously and the computer system executes instructions at maximum speed. Usually, sufficient power is available to the computer in order to continue execution at all times. Power consumption is generally a secondary consideration to these real-time monitoring and control functions. Therefore, these types of systems have typically been implemented using TTL (transistor-transistor logic) dynamic logic devices instead of CMOS (charged metal oxide semiconductor) static logic devices because dynamic devices require less area, are cheaper, and operate sufficiently fast for most real-time applications.
In other applications, continuous real-time monitoring and control is not required. In some control systems, for example, action by the computer need only take place at infrequent intervals of time. One such example is that of the temperature sensor microcontroller which is coupled to an environmental control system in a building. For a temperature sensor, the building temperature may only need to be sampled at intermittent intervals (for example, once every five minutes) in order to issue the necessary signal to the heating/cooling system to compensate for variations in temperature. In this case, intermittent sampling is sufficient because instantaneous response to fluctuations in temperature is not necessary (hopefully the building will retain the temperature from a previous heating or cooling cycle for a certain interval of time). For the most part, because this unit remains idle between samples, and because on-board battery power may be used, it is desirable to put the computer into a mode where minimum power is consumed. This will allow operation in environments where power usage should be minimized, such as in an automobile. In an environmental control application for a building, for example, because many control units may be distributed throughout an entire system, power consumption for the system may be reduced.
Dynamic logic LSI (large-scale integrated) circuits are typically used in computers due to their low cost, small area requirements, and adequate performance for most applications. Dynamic logic devices, and memories in particular, use charged capacitors which must be recharged at regular intervals due to capacitor leakage. Dynamic logic devices therefore require the use of "refresh" circuitry in order to recharge these capacitors at certain minimum intervals to retain their data. A minimum refresh frequency for some dynamic memory devices (DRAM) is approximately 500 kilohertz (KHz). Because a computer comprised of dynamic logic components requires the use of refresh circuitry which operates continuously to retain the data, power is used constantly even when no instructions are being executed by the computer system. Moreover, because these devices must be refreshed at regular intervals, a system clock must be maintained. This clock also consumes power, even when no instructions are being executed. In an application which requires minimum power consumption, such as one powered by a battery and/or one which does not operate continuously, the use of dynamic logic devices along with the required clock and refresh circuitry provides a design that consumes more power than might otherwise be desired.